MELIFE5pcs BMS 4S 25A 16.8V Battery Protection Board for Lithium Battery Protection Circuit Charging Board Module Integrated Circuits.

I used this board to manage 5 high-current 21700 batteries. I can draw 20A from it at 18v until the batteries reach 2.85v cut off voltage.It will also charge the batteries are 5A with no problem and cuts the charging off at 4.22v/cell.Very nice product for the price. I will be using one for another battery project soon.

The integrated circuit used in the board does not support cells balancing.There are two types of BM3451 integrated circuit, the version B in TSSOP20 package and used in this product does not provide BMS functionality.This product is falsely advertised as BMS!You can still use this product to protect your battery but you will need to balance the cells using something else.

I made the poor choice to replace the cells of a dying battery pack for a Shark stick vacuum. I did not want to just throw the whole thing away and spend $80+ on a new pack when the first one was failing after less than a year. It was a pain. The Shark people made this intentionally painful it seems. I've never had a harder time getting a battery taken apart.I got this BMS because the original Shark BMS failed after I disconnected it. Malice or just crummy BMS, nobody knows, but it failed.I had no idea what I was doing when I bought this, just nosed around and hoped for the best. Seems to be working fine in the vac, batteries are charging/discharging, etc. The one thing I could not find any information on is if this BMS does balancing. Still no idea, I do not have the tools to test.The only thing that threw me for a loop is the odd labeling on the solder pads. Most 4s BMS will label the terminals as B1, B2, B3, etc. This one has B=B1, B1=B2 and B2=B3. I guess if you think that B=B0 it kind of makes sense, but every other BMS I looked at doesn't use this sequence. Just be aware when you're connecting up and you'll be fine.

i use these to upgrade my cordless drill battery packs

Does what it says. You will need to add your own balance circuit board. You charge and discharge from the same soldering point. Seems to be well built for the price.Edit to my last post. Out of the 5 I got only 3 worked. 2 only output was 6v. Not 16.8v